As leaders from around the world meet in Copenhagen to address global climate change this month, we thought it was a good time to reflect on our own carbon footprint. In 2007, we committed to become a carbon neutral company. We know that it isn't possible to write a check and eliminate the environmental impact of our operations. So what does “carbon neutrality” mean to us?

First, we aggressively pursue reductions in our energy consumption through energy efficiency, innovative infrastructure design and operations and on-site renewable energy. Our Google designed data centers use half the energy of typical facilities. We're also working to accelerate the development of economic, clean renewable energy at scale through research and development, investment and policy outreach. At this time, however, such efforts don't cover our entire carbon footprint. Therefore, since 2007 we've gone a step further and made a voluntary commitment to buy carbon offsets to cover the portion of our footprint that we cannot yet eliminate — which is what we mean by "carbon neutrality."

So what exactly is a carbon offset? The idea behind an offset is that we pay someone to reduce their greenhouse gas emissions in a specific, measurable way, thus offseting an equal climate impact on our side. To determine our impact, we calculate our annual carbon footprint, which is then verified by an independent third party. We include direct energy consumption (like natural gas) and electricity use, employee commuting, company vehicle use, business travel and estimates of carbon emissions from building construction and from the manufacturing of servers used in our datacenters. We then buy an equivalent number of carbon offsets.

While carbon offsets seem simple in principle, in practice they are surprisingly complicated. In particular, it's often difficult to say whether or not the offset project results in emissions reductions that would have happened anyway. We find ourselves asking whether the project in fact goes beyond "business as usual." In the world of offsets, this concept is referred to as "additionality." Carbon offsets have a mixed reputation because some projects are not additional. Here at Google, we have set a very high bar to ensure that our investment makes an actual difference in reducing greenhouse gas emissions by purchasing offsets that are real, verifiable, permanent and additional.

To date, we have selected high quality carbon offsets from around the world that reduce greenhouse gas emissions — ranging from landfill gas projects in Caldwell County, NC, and Steuben County, NY, to animal-waste management systems in Mexico and Brazil. Our funding helps make it possible for equipment to be installed that captures and destroys the methane gas produced as the waste decomposes. Methane, the primary component in natural gas, is a significant contributor to global warming. We chose to focus on landfill and agricultural methane reduction projects because methane's impact on warming is very well understood, it's easy to measure how much methane is captured and the capture wouldn't happen without our financing (for the projects we're investing in, they couldn't make enough money selling the gas).

We need fundamental changes to global energy and transportation infrastructure to stabilize greenhouse gas emissions over the long term. In the meantime, the projects to which we contribute offer measurable emissions reductions and allow us to take responsibility for our carbon footprint. To that end, we're always looking for good emissions-reduction projects to support. If you have a landfill gas or agricultural methane carbon offset project you think we should consider, please visit this page for more information about how to participate in our latest carbon-offset procurement round.